This invention relates to a casing for shaped explosive charges for use in perforating oil and gas wells, and its method of manufacture.
The use of shaped charges for perforating in oil wells is well known. Such shaped charges include a bell shaped housing or casing into which is inserted a cone shaped liner with explosive material therebetween. The shaped charge is then located in the tubular housing of a perforating gun and oriented such that when the explosive is detonated the conical liner is destroyed and a jet is formed which is directed through a port in the housing of the gun to perform the desired perforating.
In a nonexpendable gun the port is sealed with a replaceable plug such that after perforation the gun assembly may be retrieved and new shaped charges and port plugs may be installed such that the gun assembly may be reused.
The explosions of the shaped charge to perform the perforating operations tends to cause swelling and distortion in the gun housing. Because of these distortions, the life of the gun housing may be shortened such that the gun housing must be discarded after a few uses.
Several attempts in the past have been made to reduce damage to the gun housing without affecting the performance of the shaped charge. One such attempt to increase the life of the gun housing is shown in U.S. Pat. No. 3,282,354 to Hakala et al. wherein a double walled case was used around the shaped charge.
In the past, pressed metal liners have been used for insertion into a machined steel casing to form the shaped charge.
In the present invention a pressed powdered metal casing is disclosed for use with a shaped charge in an oil well perforating gun, which casing is destroyed with the detonation of the explosive material. It has been found that use of the pressed powder metal casing results in less distortion and damage to the perforator gun housing.
It has also been found that the pressed metal casing is reduced to a powder by the explosion of the shaped charge. This powder is easily removable from the perforator gun housing when the housing is being cleaned for reuse.
It has further been found that the use of heavier metals in the pressed metal casing for the shaped charge results in deeper perforations than when a lighter metal, for instance iron, is used. It has also been found that when a lighter metal such as iron is used, less distortion of the perforator gun housing results.
Also disclosed is a molding apparatus and components of a powdered metal mix which may be used in forming the shaped charge housing of the invention.